Mobile telephony networks (PLMNs) were initially conceived for enabling voice communications, similarly to the wired, Public Switched Telephone Networks (PSTNs), but between mobile users, or between a mobile user and a fixed (wired) user. Wireless communications networks have experienced an enormous spread, especially after the introduction of second-generation mobile cellular networks, and particularly digital mobile cellular networks such as those complying with the Global System for Mobile communications (GSM) standard (and its United States and Japanese counterparts).
The services offered by these cellular networks in addition to plain voice communications have rapidly increased in number and quality; just to cite a few examples, services like the Short Message Service (SMS) and the Multimedia Message Service (MMS) services, and Internet connectivity services have been made available in the last few years.
However, these second-generation cellular networks, albeit satisfactory for voice communication, offer very poor data exchange capabilities.
Similarly to the PSTNs, second-generation cellular networks are in fact Circuit-Switched (CS) networks; this greatly limits the bandwidth that can be allocated for a given user. On the contrary, data communications networks such as computer networks and, among them, the Internet, adopt Packet Switching (PS) schemes, which allow for extremely higher data transfer rates.
Some solutions have been proposed to overcome the limitations of conventional, CS cellular networks such as the GSM networks, so as to enable users of mobile terminals efficiently exploiting services offered through the Internet. One of the solutions that have acquired a significant popularity is the General Packet Radio Service (shortly, GPRS). The GPRS is a digital mobile phone technology compatible with GSM networks (actually, built on the existing GSM network architecture) that enables data transfer at a speed higher than that allowed by pure GSM.
Essentially, the GPRS (and its evolution called Enhanced Data rates for Global Evolution; shortly, EDGE) is a GSM add-up that supports and enables packet-based (i.e., PS) data communication. The GPRS, being an almost ready-at-hand solution for enhancing the data exchange capabilities of already existing GSM networks, is gaining certain popularity.
Quite concisely, a GPRS network includes at least one Gateway GPRS Support Node (GGSN) acting as an interface between the mobile telephony network and one or more external packet data network, such as the Internet. The GGSN exchanges data packets, through a GPRS backbone network, with one or more Serving GPRS Support Nodes (SGSN); the generic SGSN routes the data packets received, through the GGSN and the GPRS backbone network, from the external packet data network, to the proper destination user's mobile communication terminal (commonly referred to as a mobile station).
In order to provide packet-based data communications services, the Base Station Controllers (BSCs) of the mobile telephony network (the network entities that control the network's radio stations, the so-called Base Transceiver Stations—BTSs) are associated with respective packet handling apparatuses known as the Packet Control Units (PCUs). The generic PCU is thus usually associated with a plurality of respective network's cells, and behaves as an interface of the respective BSC to a respective SGSN: it converts the data packets, received from the SGSN and directed to the destination mobile terminals located in the network cells of the associated plurality, into data streams adapted to being transmitted “over the air”, by the proper network BTS, exploiting the radio resources of the network, and, dually, the PCU converts data streams transmitted by the mobile terminals “over the air” and received by the BTS into properly formatted data packets, for the transmission to the SGSN and GGSN.
The GPRS system's physical level is based on the GSM one, superimposing thereto a different logic structure. Control and data traffic “logic” channels are multiplexed in time and frequency division on a single GPRS physical channel, called Packet Date CHannel (PDCH). A PDCH corresponds to a physical GSM channel, and it is defined, in the frequency domain, by one of the GSM radio carriers, and, in the time domain, by one of the GSM time slots. Over a generic PDCH, one or more GPRS/EDGE connections may be established.
The generic PCU has resources for managing the interface (so-called Gb interface) with the SGSN, and resources for managing the interface with the radio front-end of the network, i.e. the BSCs and the BTSs.
The resources provided in the generic PCU for managing the interface towards the radio front-end can be described as composed of a collection of elementary resource units; for the purposes of the present invention, by resource unit there is intended the elementary, minimum set of resources of the PCU that are treated as an unique entity and that can be allotted as a whole for the management of a PDCH.
Within the generic PCU, one or more resource units may be univocally assigned to a single PDCH. The association between the one or more PCU's resource units and the PDCH is in general released when the GPRS data connection(s) that required the assignment of PCU resources are terminated, and the PDCH is released.
It appears that there is a strong correlation between the PCU's overall capability to handle data packet connections, and the variability in time (in terms of both offered traffic and length of the single call) of the data connections on the radio interface.
The dimensioning of the PCUs' resources, particularly the number of elementary resources for managing the interface towards the radio front-end of the network, is thus a critical aspect of the design of a GPRS network, especially in consideration of the foreseeable increase in time of the GPRS and EDGE users, also due to the increase in number and quality of the PS services offered.
Manufacturers of network apparatuses usually carry out the dimensioning of a PCU from the viewpoint of the number of elementary resources to be provided based on empirical approaches, which are essentially based on the knowledge of the number of installed radio resources (i.e., the number of installed FDMA/TDMA radio carriers) of the radio front end of each network cell coupled to the PCU being dimensioned.